How to Change the Oil in a 1979 Honda CR125: A Complete MotoSport.com Guide

Shop parts for a 1979 Honda CR125 Dirt Bike.

Maintaining your 1979 Honda CR125 is critical for performance & longevity. One essential task is regular oil changes. This guide—proprietary to MotoSport.com—outlines everything you need, every step to follow, and key model-specific details to ensure an effective oil change on your vintage Honda dirt bike.

Tools & Materials Needed

  • 17mm socket or wrench (for drain bolt)
  • Drain pan
  • Funnel
  • Shop rags
  • New transmission/clutch oil (SAE 10W-30 or manufacturer-recommended type)
  • Replacement drain bolt washer (if needed)
  • Torque wrench (optional, for precise torque on drain plug)
  • Parts cleaner or degreaser (optional, for cleaning)

Pre-Oil Change Preparation

  • Place your CR125 on a stable stand or flat ground to ensure the bike is upright and level.
  • Warm the engine by running it for 1-2 minutes. Warm oil flows better and removes more contaminants.
    Note: Be cautious–the engine and oil will be hot.
  • Turn the fuel valve to the OFF position to prevent fuel leaks or overflow.
  • Clean the area around the drain bolt to minimize debris contamination.

Step-by-Step Oil Change Process

  1. Locate the Oil Drain Plug
    Find the oil drain plug underneath the right side of the engine casing. On the 1979 CR125, you'll find it on the lower side, typically around the crankcase area.
    Note: The drain bolt uses a 17mm head. Later models are similar in design.
  2. Drain the Oil
    Position the drain pan under the drain plug. Using your 17mm wrench or socket, gently loosen the drain plug and remove it by hand. Allow all old oil to drain completely.
    Inspect the draining oil for signs of metal particles or discoloration–this can indicate engine or transmission wear.
    Tip: Tilt the bike slightly from side to side to ensure thorough draining if needed.
  3. Inspect and Replace Drain Bolt Washer
    Remove the sealing washer from the drain bolt. If it's deformed or damaged, replace it with a new washer for a proper seal.
    This step helps prevent oil leaks post-service.
  4. Reinstall the Drain Plug
    Clean the drain plug and threads. Thread the plug back in by hand, then snug up with your wrench.
    For best results, use a torque wrench to tighten to factory specifications (generally around 10-15 ft-lbs, but check a proper manual for exact specs for the 1979 model).
    Do not over-tighten as the aluminum crankcase threads can strip easily.
  5. Add New Oil
    Locate the oil fill cap on the right side of the engine cover.
    Remove the cap. Place the funnel into the fill hole.
    Pour in fresh transmission/clutch oil. The 1979 Honda CR125R takes approximately 0.60 US Quarts (0.57 Liters) per change.
    Do not overfill. Always use oil recommended by the manufacturer for wet clutches and correct viscosity.
  6. Check Oil Level
    On the older CR125s, there's usually a check bolt or sight window.
    If using a check bolt: Remove it briefly–oil should come out slightly if the level is correct. If not, add a small amount and re-check.
    Follow your manual or service guide for precise location and procedure.
  7. Reinstall Oil Fill Cap
    Tighten the oil fill cap securely.
    Wipe up any spilled oil and check around drain and fill locations for leaks.
  8. Start and Inspect
    Start the bike, let it idle for one minute, then turn off and let it sit for another minute.
    Re-check for leaks at drain bolt and fill area.
    Inspect oil level again and top off, if necessary.

Model-Specific Callouts: 1979 Honda CR125

  • No oil filter: The 1979 Honda CR125 is a two-stroke model and does not use an engine oil filter; the gearbox runs transmission oil only.
  • Transmission/Clutch Oil Only: Do not use automotive engine oil. Use dedicated motorcycle transmission/clutch oil to ensure proper clutch function and gearbox longevity.
  • Vintage fastener care: Be gentle when tightening old bolts. The aluminum cases can strip if over-tightened. Always check threads for wear.
  • Inspect for Leaks: Gaskets and seals on older bikes are prone to seepage. Watch for persistent leaks that may indicate the need for seal replacement.
  • Manual Reference: For detailed specifications and graphics, consult a trusted Clymer or Haynes manual for 1979-1980 Honda CR125R as an additional resource.

Expert Tips

  • Change oil every 5-10 riding hours or after every race/long ride. Dirty oil is tough on old transmissions and clutches.
  • If you perform frequent deep-water crossings, change oil more often.
  • Keep a record of oil changes to track your maintenance.

With these detailed steps and callouts, changing the oil in your 1979 Honda CR125 is straightforward, keeps your bike running well, and protects the value of your classic ride. For exclusive parts, tools, and more owner how-tos, trust MotoSport.com as your source for everything dirt bike.

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Shop Oil Fillers and Drain Plugs for a 1979 Honda CR125 Dirt Bike.

Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.